Per Mertesacker is entrusted with the job of collecting fines from Arsenal players in breach of club discipline but the German may find himself going cap in hand to manager Arsene Wenger for his place in the team.

Andy Murray crashed to world number one Novak Djokovic in another dramatic encounter at the O2 Arena this afternoon.

Murray was brilliant in the first set but could not sustain it and a third-set comeback eventually counted for nothing as Djokovic ran out a 4-6 6-3 7-5 winner.

The defeat means world number three Murray has his work cut out to qualify for the semi-finals at the Barclays ATP World Tour Finals.

But his victory over Tomas Berdych on Monday means he still has a good chance of reaching the last four, with his final Group A clash to come against Jo-Wilfried Tsonga in two days' time.

Djokovic's progress will be assured if Tsonga beats Berdych in tonight's match.

Murray and Djokovic were meeting for the seventh time this year after sharing the first six, with Djokovic winning an epic Australian Open semi-final but Murray turning the tables at the Olympics and then clinching his first grand slam title at the US Open.

The O2 crowd, packed almost to 17,000 capacity, were anticipating another classic and were certainly not disappointed in the opening game.

Murray brought up a break point and took it with a scampering cross-court forehand after the sort of rally for which the pair have become famous.

Djokovic did not win a point on Murray's serve until a double fault in the sixth game, and in the ninth game he found himself facing set point after some more incredible defence from the third seed followed by a cute drop shot.

He could not convert that one, hooking a forehand long, but on serve he was rock solid once more, holding to love after 44 minutes.

Murray had another chance to break in the third game of the second set but Djokovic landed a drive volley right on the join of the lines, and three games later he had his first chance.

Surprisingly Murray chose to serve and volley on break point and it did not pay off, the Scot forced to play off his toes and missing the baseline by a fraction. And this time it was Djokovic who did not waver serving it out.

The momentum had well and truly shifted, with Djokovic now the aggressor and Murray throwing in a few too many errors. Four of them cost him in the third game of the decider as the top seed broke through again.

The crowd tried to raise their man but the contrast from the first set was total and Murray, whose serves were now coming back with interest, was beginning to look a little forlorn.

Instead of putting pressure on Djokovic, Murray was just trying to hang on, and he saved break points in the fifth and seventh games before at last rediscovering his spark.

He forced himself to flatten his forehand back out and it paid dividends, HawkEye showing Djokovic to have missed by a whisker to give Murray the break back, and suddenly the British player was one game away.

Djokovic held firm, though, and it was Murray who cracked again to leave his opponent serving for the match.

Still it was not straightforward as Murray forced two more break points but this time Djokovic saved them and clinched victory after two hours and 34 minutes when the Scot missed a backhand.